How do invasive pests affect interactions between members of pre-existing agrosystems? The invasive pest Drosophila suzukii is suspected to be involved in the aetiology of sour rot, a grapevine disease that otherwise develops following Drosophila melanogaster infestation of wounded berries. We combined field observations with laboratory assays to disentangle the relative roles of both Drosophila in disease development. We observed the emergence of numerous D.&nbsp;suzukii, but no D.&nbsp;melanogaster flies, from bunches that started showing mild sour rot symptoms days after field collection. However, bunches that already showed severe rot symptoms in the field mostly contained D.&nbsp;melanogaster. In the laboratory, oviposition by D.&nbsp;suzukii triggered sour rot development. An independent assay showed the disease increased grape attractiveness to ovipositing D.&nbsp;melanogaster females. Our results suggest that in invaded vineyards, D.&nbsp;suzukii facilitates D.&nbsp;melanogaster infestation and, consequently, favours sour rot outbreaks. Rather than competing with close species, the invader subsequently permits their reproduction in otherwise non-accessible resources and may cause more frequent, or more extensive, disease outbreaks.

Mentions:
We conducted trials to determine whether four exposure treatments (D. suzukii, D. melanogaster, both species or nothing) could trigger sour rot on a pristine grape berry. Exposure treatment had a significant effect on the presence of sour rot symptoms (χ2 = 24.96; p < 0.0001; figure 2), but not on grey rot development where 15% of grapes had grey rot distributed equally among treatments (χ2 = 0.47; p = 0.92). The two treatments with D. suzukii females (i.e. D. suzukii and Both species) induced sour rot symptoms more frequently than in the absence of D. suzukii (Odds ratios; p < 0.0039). When limiting the analysis to grapes exposed to D. suzukii females, all berries with eggs exhibited sour rot symptoms while only 15% of them did in the absence of visible eggs (χ2 = 21,23; p < 0.0001).Figure 2.

Mentions:
We conducted trials to determine whether four exposure treatments (D. suzukii, D. melanogaster, both species or nothing) could trigger sour rot on a pristine grape berry. Exposure treatment had a significant effect on the presence of sour rot symptoms (χ2 = 24.96; p < 0.0001; figure 2), but not on grey rot development where 15% of grapes had grey rot distributed equally among treatments (χ2 = 0.47; p = 0.92). The two treatments with D. suzukii females (i.e. D. suzukii and Both species) induced sour rot symptoms more frequently than in the absence of D. suzukii (Odds ratios; p < 0.0039). When limiting the analysis to grapes exposed to D. suzukii females, all berries with eggs exhibited sour rot symptoms while only 15% of them did in the absence of visible eggs (χ2 = 21,23; p < 0.0001).Figure 2.

How do invasive pests affect interactions between members of pre-existing agrosystems? The invasive pest Drosophila suzukii is suspected to be involved in the aetiology of sour rot, a grapevine disease that otherwise develops following Drosophila melanogaster infestation of wounded berries. We combined field observations with laboratory assays to disentangle the relative roles of both Drosophila in disease development. We observed the emergence of numerous D.&nbsp;suzukii, but no D.&nbsp;melanogaster flies, from bunches that started showing mild sour rot symptoms days after field collection. However, bunches that already showed severe rot symptoms in the field mostly contained D.&nbsp;melanogaster. In the laboratory, oviposition by D.&nbsp;suzukii triggered sour rot development. An independent assay showed the disease increased grape attractiveness to ovipositing D.&nbsp;melanogaster females. Our results suggest that in invaded vineyards, D.&nbsp;suzukii facilitates D.&nbsp;melanogaster infestation and, consequently, favours sour rot outbreaks. Rather than competing with close species, the invader subsequently permits their reproduction in otherwise non-accessible resources and may cause more frequent, or more extensive, disease outbreaks.